1. Field of the Invention
The present invention relates to a gate valve, particularly to a non-rubbing gate valve that is employed for opening and closing, e.g. for carrying in and out objects to be treated, such as semiconductor wafers and liquid crystal substrates.
2. Description of the Prior Art
A gate valve of this kind is employed in a semiconductor-manufacturing field, liquid crystal-manufacturing field or similar field. For example, it is used as a partition of a load lock chamber, transfer chamber or reactor of a CVD apparatus. In a semiconductor-manufacturing apparatus, cleanliness is required, and thus the generation of particles or the like has to be particularly suppressed. In a gate valve for a semiconductor-manufacturing apparatus, a valve-side seat surface is rubbed against a flow passage-side valve seat surface, and the generation of particles or dust may be increased. Therefore, countermeasures for preventing the rubbing between the valve-side seat surface and the flow passage-side valve seat surface are generally taken.
As a countermeasure, in a gate valve for a semiconductor-manufacturing apparatus, a valve body is integrally provided with a valve rod, and a cam or link is provided at the valve rod to attempt to make the valve body non-rubbing. Particularly, upon the actuation of such a gate valve, first, the valve rod is moved in a direction along its axis to move the valve body to the same height level as the flow passage port, and then, the valve body is swayed together with the valve rod using a cam or link to close the valve.
To be specific, a known two-cylinder structure comprises a cylinder that moves a valve rod in a direction along its axis and another cylinder that moves the valve body in a direction orthogonal to the valve rod to close the valve. Meanwhile, a one-cylinder structure is also known, in which a cylinder moves a valve rod in its axial direction and then, by means of a cam or link incorporated in a valve body, moves the valve body in a direction orthogonal to the axial direction of the valve rod to close valve.
Of these, there has been proposed, as a gate valve of the latter one-cylinder structure, the gate valve having a structure in which a valve body is moved toward a flow passage, i.e. in a direction orthogonal to the movement direction of a valve rod, by means of a piston and a cam or link that are incorporated in the valve body (Japanese Patent No. 3323459, for example).
The prior art gate valve is provided with a displacement mechanism that displaces a valve disk formed in a valve box for opening and closing a flow passage, in a direction substantially orthogonal to the axis of a valve rod. The displacement mechanism comprises a box that is fixedly attached to an end of the valve rod, a displacement member provided to be displaceable within the box, a connection member that is connected to the valve disk and a pin member that is engaged in a long hole formed in the displacement member. Upon actuation, the valve disk is moved in a direction perpendicular to the valve rod and toward the flow passage by the action of a cam of the displacement mechanism.
In a gate valve having the former two-cylinder structure, a valve body is moved in a direction orthogonal to a valve rod, thereby attaining sealing from a direction orthogonal to the flow passage. However, the structure assumes complexity due to the existence of increased number of cylinder structure to thereby elevate the cost, which is problematic.
In the gate valve having the latter one-cylinder structure, a cam or link is incorporated in the valve body to enable the valve body to be rotated in a direction orthogonal to the axial direction of the valve rod. Therefore, when the valve body is to be rotated after the valve rod is moved in a direction for closing the valve, the rotation movement assumes a circular arc movement. This applies force to an O-ring, which is provided at the valve body for sealing, in a direction to cause distortion of the O-ring, which is problematic. Meanwhile, in the course of rotation of the valve body for opening the valve, force is applied to the O-ring in a direction causing distortion thereof in the same manner as in the case of closing the valve. Particularly when the valve is kept in a closed state over a long period of time, O-ring is adhered to the valve seat surface in some cases. In such cases, greater force that causes distortion is applied to the O-ring, resulting in possible dropout of the O-ring. As described above, the prior art gate valves fail to achieve a target object to provide non-rubbing gate valves, and great distortion force is applied to the O-ring upon either opening or closing the valve. Thus, particles are readily generated, the product service life becomes short, and there is a possibility of the O-ring being dropped out.
Meanwhile, in a gate valve of the Japanese Patent No. 3323459, a box is provided outside a displacement mechanism on purpose. Accordingly, the structure of the displacement mechanism tends to be complex and large in size.
The present invention has been developed in order to solve the conventional problems, and an object of the present invention is to provide a gate valve in which a sealed portion is not rubbed upon opening and closing of the valve, and distortion or dropout of a seal member is not caused to make it possible to suppress generation of particles or dusts and reliably maintain the sealing property over a long period of time even when opening and closing operations of the valve is repeatedly carried out.